DESCRIPTION: (Applicant's Abstract) The objective of the proposed experiments is to determine the effects of acute morphine treatment on in vivo immune function. To achieve these goals, the proposed research investigates immunological changes in inflammation and cytokine levels following induction of the delayed type hypersensitivity (DTH) response following acute morphine administration. Specific Aim I assesses the specificity of morphine's effects by administering morphine at distinct time points across a range of doses. The pharmacological specificity of morphine's effects is assessed in Specific Aim II by the administration of the opiate antagonist naltrexone prior to morphine treatment. The involvement of central verus peripheral opioid receptors is explored in Specific Aim III by central and peripheral administration of N-methylmorphine, a drug which does not penetrate the blood brain barrier. To determine whether the central effects parallel systemic administration, naltrexone is also administered prior to drug treatment. The results of these studies will expand upon the in vitro assessments of morphine's effects on immune function and provide clarification of the immunomodulatory effects of morphine on an intact organism.